TABLE OF CONTENTS Kevin D. Wills, M.S.E., P.E.
Consulting Engineer
Stanley Consultants, Inc.
Domestic wastewater with an average daily flow of 4.0 Mgd (15,140 m 3/d) has a five day Biochemical Oxygen Demand (BOD 5) of 240 mg/L after primary settling. The effluent is to have a BOD 5 of 10 mg/L or less. Design a complete-mix activated sludge reactor to treat the wastewater including reactor volume, hydraulic retention time, quantity of sludge wasted, oxygen requirements, food to microorganism ratio, volumetric loading, and WAS and RAS requirements.
1. Compute the reactor volume
The volume of the reactor can be determined using the following equation derived from Monod kinetics:
where <i class="emphasis">Vr </i>= Reactor volume (Mgal) (m<sup3</sup>)<i class="emphasis"> <span class="unicode">?</span></i><sub<i class="emphasis">c</i></sub> = Mean cell residence time, or the average time that the sludge remainsin the reactor (sludge age). For a complete-mix activated sludge process,<i class="emphasis"> <span class="unicode">?</span></i><sub<i class="emphasis">c</i></sub> ranges from 5 to 15 days. The design of the reactor is basedon <i class="emphasis"><span class="unicode">?</span></i><sub<i class="emphasis">c</i></sub> on the assumption that substantially all the substrate (BOD) conversionoccurs...
